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March 26, 2017

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Hey :)
I was wondering if someone could tell me if this answer and working is correct or not...

Cos theta =-0.25
Cos inverse -0.25 = -14
therefore theta equals:
180--14=194or/and
180+-14=166

Any help would be much appreciated :)
Thanks!

  • Maths - ,

    cos (theta) = -0.25
    theta = cos^-1 (-0.25)

    there are two answers:
    theta = 104.48 degrees = 3.65 radians
    and,
    theta = -104.48 degrees = -3.65 radians

    hope this helps~ :)

  • Maths - ,

    Usually the required angles are in the domain of
    0 ≤ Ø ≤ 360°

    Since the given cosØ is negative, by the CAST rule,
    Ø must be in either quadrant II or III
    from cosØ = +.25 we get the reference angle of 75.52°
    so Ø = 180°-75.52° or 104.48° (Jai's answer)
    or Ø = 180°+75.52° or 255.52°

    Since the period of cosØ is 360°, you can get other answers by adding or subtracting multiples of 360°
    (For Jai's second answer, 255.52 - 360° = 104.48°)

    I have no idea how you came up with
    inverse cos (-.25) = -14

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